The present invention relates to a three-dimensional vision system which recognizes the three-dimensional shape of an object by the use of slit-like light segmentation when the object is subjected to the operations of assembly etc. in a robot, an automaton etc.
Prior-art vision sensors which apply light segmentation are, for example, CONSIGHT published by General Motors in U.S. (literature: M. R. Ward et al, "CONSIGHT An Adaptive Robot with Vision", Robotics Today, pp. 26-32 (Summer, 1979)) and a compact robot vision published by Hitachi Ltd. (literature: Nakagawa et al, Structured light method for inspection of solder joints and assembly robot vision system: Proc. of 1st Int. Symp. of Robots Res. Bretton Woods, Aug. 28-Sept. 2, '83). In a case where the surface of an object to be seen is liable to irregularly reflect light and where external light conditions are stable, such a vision sensor based on the light segmentation system can receive a clear image and is therefore a very excellent system capable of three-dimensional image inputing. However, in a case where the object to be handled has a blackish surface liable to absorb light or where it has a reflectivity close to the total reflection, the quantity of light to enter the image sensor is comparatively small, and the extraction of a light segmentation line has been difficult under the influences of a background image etc. The reason why the extraction of the light segmentation line becomes difficult when the reflected light entering the image sensor lessens due to the properties of the surface of the object to-be-handled, is that a background object brighter than reflected light from the light segmentation line on the object to-be-handled becomes prone to appear in an image screen due to illumination based on external light.
Moreover, in a case where the fluctuation of external light is great, a segmentation decision threshold value in a light segmentation line extracting circuit fluctuates greatly, and stable light segmentation line extraction has been difficult. The reason is that, since the input image from the image sensor has a brightness obtained by adding up the light segmentation illumination and the external light illumination, the threshold value for deciding the segmentation line must be sharply changed on account of the fluctuation of the external light.